It began with a cryptic 911 call from Denise Closs's cell phone. No one spoke directly to the police dispatcher, who heard distant voices and loud commotion before the call ended.

When authorities arrived four minutes later at the Barron, Wisconsin, house, they found Closs and her husband, James, shot to death inside their home and the couple's 13-year-old daughter, Jayme, missing.

The phone from which the call was made lay on the floor inside the modest, taupe-colored home.

"The phone isn’t near anyone so I don’t know if it got kicked," Sheriff Chris Fitzgerald of Barron County told Fox News on Tuesday. "It was closer to Denise than to James."

"No one talked on that call and we don't know who made it. We heard voices but we can’t make out what was said," he said, adding that it sounded as though the call was made in a room separate from the commotion.

"We do believe Jayme was home at the time the call was made," Fitzgerald noted.

With no suspects, no sighting of the child and scarce physical evidence one month after the Oct. 15 murders, police in the small town of Barron are scrutinizing the few clues they have, starting with the mysterious 911 call and a front door riddled with bullet holes.

Fitzgerald would not say whether the killer shot through the door but local news footage shows investigators carrying it away from the scene -- covered with what looks like bullet holes. Fitzgerald confirmed to Fox News that the door was undergoing forensic analysis. He also would not elaborate on the type of gun used in the crimes, citing the sensitivity of the investigation. James Closs kept hunting rifles inside the home but all have been accounted for.

"There’s not a lot of physical evidence," he said. "We took the door and anything that they [the killer] possibly could have touched."

Both mother and daughter attended a family birthday party at around 4 p.m. on Oct. 14 at the home of Denise Closs's sister, Jennifer Smith, who lives on the other side of town. At around 10 p.m. that night, Smith spoke with Closs by phone from her home. Nothing appeared amiss, according to family and police.

"At 10 p.m. we know everybody was at the house and accounted for," Fitzgerald told Fox News.

At just past 1 a.m. local time on Oct. 15, the 911 call was placed to the sheriff’s office from Denise Closs's cell. When the call ended abruptly, a dispatcher called the landline at the family's home but it was disconnected.

Police arrived four minutes after the initial call to the Closs home on Highway 8 and found the body of James Closs in the front doorway; his wife's was inside the home. There was no sign of Jayme, except for her cell phone, which was reportedly found plugged into an outlet in the kitchen.

The motive of the crime remains elusive. With two parents dead, their young daughter missing and no obvious sign of theft at the home, investigators are struggling to answer a key question: Why?

"I’m really looking to see if they were targeted or if it was a random attack," Fitzgerald said. "This is the question I think about every night before I go to bed."

"It appears targeted but I can't 100 percent say that it is," he said. "And I don't know who the target was."

Relatives of the Closs family, meanwhile, said they are conviced the brutal murders and apparent abduction were carefully planned.

"If this was random, it wouldn't -- there'd be more evidence," Steve Naiberg, the girl's uncle, said in an exclusive interview Monday with Fox affiliate KMSP-TV and other family members.

"I think this was targeted -- planned," said Suzi Allard, Jayme's aunt.

A relative described Denise Closs to Fox News as the "family angel." The 46-year-old mother "would take off work days if you needed help," said the relative, who wished to remain anonymous.

The family also strongly refuted a local rumor that Jayme -- described as quiet and well-liked -- had a secret, older boyfriend, according to the station.

“We just want Jayme home," added Smith. "We want to know why all of this happened -- just wish we had some answers and hoping for that miracle of Jayme coming home."

Fox News' Matt Finn contributed to this report.